As with many breakthrough LED applications, the journey started with a thorough understanding of the specifications from the first principles.
In this case, the challenge was to precisely illuminate the road sign and nothing else, with a tight specification on both absolute illumination (lux on the sign) and range of illumination (light/dark area ratio). Ray tracing CAD software was used to model the illuminance iteratively, and appropriate LEDs were selected along with off-the-shelf optics.
Trials were conducted with a calibrated CCD imaging camera that could automatically capture hundreds of illuminance measurements in a single frame offering super-efficient optical metrology. We rapidly completed the electronics and mechanical designs of the first-generation systems to allow for quick volume manufacture.
Second-generation LED road sign illuminations were later enabled with the simultaneous adoption of 3 innovative technologies:
Multi-die small form factor LEDs
While ‘driverless’ electronics can drastically reduce cost and increase reliability, there is usually a significant reduction in efficiency. This issue was balanced out by the design of full-custom optics.